The present invention relates to filters, particularly for irrigation purposes, but also applicable to other industrial or domestic uses.
Modern agricultural irrigation is mostly based on drip irrigation systems, which requires the water to be free of particles and other impurities that will tend to clog the system. The same applies to microjets and sprinklers irrigation. For this purpose, there have been developed various types of filters, such as metal or plastic cylindrical screen filters, or disc filters, which are based on a pack of side-by-side juxtapositioned discs, made of plastic material. The surfaces of the discs are roughened to various grades, down to a depth of only a few microns. The pack of discs is mounted on a central, cylindrical support and the whole structure is housed in a casing having inlet and outlet ports. Water is admitted at the outer circumference of the pack of discs and is made to flow between the engaging surfaces of the discs in an inwards radial direction, and discharged at the inner axial space from which it is discharged to the irrigation lines (or vice-versa). Solid particles and other impurities remain trapped between the discs. Usually a battery of, say, five to fifteen such filters are connected in parallel to feed a single irrigation main line.
The general construction and mode of operation of screen filters are similar in those respects to disc filters. Now, it is common practice to rinse every filter of the battery once in a while, to avoid its complete clogging. This is done by bypassing one of the filters of the battery and causing a reverse water flow there through. Thus, filtered water supplied by the other filters is directed under the network pressure in the opposite direction, namely from the axial space enclosed by the pack of discs (or screen) in the outwards, radial direction. Such flushing operation will cause solid particles to be ejected from between the discs (or the outer surface of the screen). This rinsing procedure is periodcally maintained, once every few hours for one or two minutes, with respect to every filter of the battery, controlled by the automatic control irrigation system.
It has however been found that--with respect to the disc filters in particular--this reverse flushing method does not provide an effective solution to the clogging problem of the filters. The reverse flushing water did not always cause the release of all solid particles from the roughened surfaces of the discs, and mainly failed to remove slimy or sticky substance accumulated therebetween. Therefore, after an extended period of time, even though the rinsing cycles were maintained, filters ceased to function properly and had to be replaced or dismantled and manually cleaned. It is thus the major object of the present invention to overcome the clogging problem of filters with reverse flushing facilities.
It is a further object of the invention to provide automatic, hydraulically-operated means for slackening the engagement between the discs of disc filters during the reverse flushing operation, and compacting same during normal operation of the filter.
It is a still further object of the present invention to have the discs or screen become rinsed by jets of water. It is a still further object of the invention to cause a spinning movement of the discs or the cylindrical screen of screen filters, during the flushing phase.